Suppression of Local Electron–Phonon Interaction in \({\pi}\)-Conjugated Oligomers and Its Monitoring Using Raman Scattering

Abstract

To effectively operate many organic electronic devices, organic semiconductors with high charge carrier mobility are required. However, in most known organic semiconductors, charge mobility is limited due to strong local electron–phonon interaction. In this work, using the example of thiophene-phenylene co-oligomers, a class of organic semiconductors that combine high charge mobility with light emission and are therefore promising for light-emitting transistors and electrically pumped lasers, the mechanism of suppression of electron–phonon interaction is studied by introducing electronegative atoms or an additional thiophene ring into the molecule. It is found that such structural modifications lead to changes in the contribution of various vibrational modes to the local electron–phonon interaction, particularly suppressing the contribution of low-frequency torsional mode. Additionally, it is shown that for two modes that contribute the most to the local electron–phonon interaction in the unsubstituted oligomer, this change correlates with their intensity in the combination scattering of light (Raman scattering, RS), confirming the potential of studying electron–phonon interaction using Raman spectroscopy. The obtained results enhance the understanding of the relationship between local electron–phonon interaction and the molecular structure of organic semiconductors, which is crucial for the targeted design of such materials with high charge mobility.